Calculating Resistance in a Circuit with Unknown Components

In summary, the question is to calculate the value of R in a circuit where the PD across a resistor is 2V and the resistance of voltmeter V1 is 10MΩ. The current flowing through V1 is 0.0000004 and the current through V2 is unknown. Using ohm's law, the resistance of the new component is determined to be 5,000,000 ohms. However, this is not the final answer as the resistance of V1 was incorrectly taken as 1MΩ instead of 10MΩ. The resistance of V2 is also relevant in calculating the current flowing through R. The final value of R can be calculated by considering the total current flow
  • #1
ravsterphysics
57
1

Homework Statement


I understand part a, but not part B.
circuit-jpg.110596.jpg


Homework Equations

The Attempt at a Solution


For part b) the PD across the resistor is 2V, but we don't know the current so we can't calculate using ohm's law eqn.

And because the new resistor's resistance is unkown, how do we actually calculate it?
 

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  • #2
You've not actually said what the question is for part b, but if it's to determine the resistance R that isn't difficult. You can calculate the currents through meter V1 and through V2, so the current through the unknown resistance will be the difference between those.
 
  • #3
Jonathan Scott said:
You've not actually said what the question is for part b, but if it's to determine the resistance R that isn't difficult. You can calculate the currents through meter V1 and through V2, so the current through the unknown resistance will be the difference between those.

shoot.

the question is: Calculate the value of R.
 
  • #4
ravsterphysics said:
shoot.

the question is: Calculate the value of R.
For part b), what can you say about the current flowing through the circuit?
 
  • #5
cnh1995 said:
For part b), what can you say about the current flowing through the circuit?

okay if V1 has voltage of 4v and its resistance is 1,000,000 ohms, then it's current must be 0.000004.

And this current must also flow through the resistor. Since total voltage is 6v, then this component must have voltage of 2V, so its resistance must be (2/0.000004) = 500,000 ohms, right?
 
  • #6
ravsterphysics said:
okay if V1 has voltage of 4v and its resistance is 1,000,000 ohms, then it's current must be 0.000004.

And this current must also flow through the resistor. Since total voltage is 6v, then this component must have voltage of 2V, so its resistance must be (2/0.000004) = 500,000 ohms, right?
Right.
But that's not the final answer. You need to find R.
Edit: Resistance of V1 is 10MΩ. You have taken it as 1MΩ..
 
  • #7
cnh1995 said:
Right.
But that's not the final answer. You need to find R.

okay the mistake I just realized is that the Mohms = 10,000,000 ohms so the current is I = 0.0000004 so resistance R is (2/0.0000006) = 5,000,000

but you're saying that's not the value of R?? But isn't the new component R??
 
  • #8
ravsterphysics said:
okay the mistake I just realized is that the Mohms = 10,000,000 ohms so the current is I = 0.0000004 so resistance R is (2/0.0000006) = 5,000,000
Yes I had edited my post immediately after posting..
cnh1995 said:
Right.
But that's not the final answer. You need to find R.
Edit: Resistance of V1 is 10MΩ. You have taken it as 1MΩ..
ravsterphysics said:
but you're saying that's not the value of R?? But isn't the new component R??
R is the resistance used in place of the 10 ohm resistor. What about the resistance of voltmeter V2?
 
  • #9
ravsterphysics said:
okay if V1 has voltage of 4v and its resistance is 1,000,000 ohms, then it's current must be 0.000004.

And this current must also flow through the resistor.

Is V2 removed for part b) ?
 
  • #10
cnh1995 said:
Yes I had edited my post immediately after posting..R is the resistance used in place of the 10 ohm resistor. What about the resistance of voltmeter V2?

CWatters said:
Is V2 removed for part b) ?

I'm still confused about what v2 has to do with the resistance of the component R? (and no, v2 is not removed)
 
  • #11
ravsterphysics said:
I'm still confused about what v2 has to do with the resistance of the component R? (and no, v2 is not removed)
What is the current flowing through the component resistance R? Is it same as that flowing through V1?
 
  • #12
ravsterphysics said:
I'm still confused about what v2 has to do with the resistance of the component R? (and no, v2 is not removed)
You need to consider the current flow. From the information available, you can calculate the current through V1 and the current through V2. The total of the currents through R and V2 must be equal to the current through V1, so the current through R is given by the difference of the two calculated currents, as I mentioned above. You then know both the potential across R and the current through it so you can calculate R.
 

FAQ: Calculating Resistance in a Circuit with Unknown Components

What is circuit resistance?

Circuit resistance is the measure of how much an electrical circuit resists the flow of electric current. It is measured in ohms (Ω) and is influenced by factors such as the type of material used in the circuit, the length of the circuit, and the temperature.

How is circuit resistance calculated?

Circuit resistance is calculated using Ohm's Law, which states that resistance (R) is equal to the voltage (V) divided by the current (I), or R = V/I. It can also be calculated using the formula R = ρL/A, where ρ is the resistivity of the material, L is the length of the circuit, and A is the cross-sectional area of the conductor.

What factors can affect circuit resistance?

Circuit resistance can be affected by a variety of factors, including the type of material used in the circuit (i.e. copper, aluminum, etc.), the length of the circuit, the temperature, and the presence of any resistors or other components in the circuit.

How does circuit resistance affect the performance of a circuit?

Circuit resistance can have a significant impact on the performance of a circuit. High resistance can cause a decrease in voltage and current, which can lead to reduced power and efficiency. It can also cause the circuit to heat up, which can potentially damage components. Lower resistance, on the other hand, allows for better flow of current and can result in improved performance.

How can circuit resistance be reduced?

Circuit resistance can be reduced by using conductive materials with low resistivity, increasing the thickness of the conductor, and minimizing the length of the circuit. Additionally, using components such as resistors and capacitors can help regulate the flow of current and reduce overall resistance in a circuit.

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